This invention relates in general to an installation for removing fats and oils, for which purpose fat and oil-degrading micro-organisms are used in particular. The installation can, in particular, be designed to simultaneously separate and remove fats and oils in waste water. The fats and oils in question may be of different types such as e.g. mineral, synthetic or organic. Of particular interest here are the type of organic fats and oils that occur in waste water from hotels, restaurants and other industrial kitchens above all. The installation can, however, also be designed for the waste water from food-processing operations of all kinds such as, for example, slaughterhouses and butchers shops.
Many local authorities impose discharge regulations on commercial users of the local sewage system in order to protect their waste water purification plants and to prevent drainage pipes from clogging up. In Germany, for example, the maximum volume of organic fats and oils which such commercial operations are permitted to discharge per liter of waste water fluctuates depending on the local authority between 50 mg and 250 mg, with a limit of 50 mg now increasingly being prescribed. This is why such businesses install fat-separating plants. In urban areas, one fat-separating plant of this type is usually operated for about every 500 residents.
Conventional fat-separating plants, which are designed to separate fats and oils from water solely by means of gravity, are associated with a series of problems. Firstly, under the greatly fluctuating operating conditions that prevail in practice, the actual fat-separating capacity of the installations is often lower than what is required to comply with the statutory limits. When determining the total content of organic oils and fats as polar lipophile substances, it is often forgotten that, because of the way fat-separators function, they can only hold back those parts of the lipophile substances that are separable. They are not capable of holding back the emulsified, dissolved and dispersed fat that occurs because of the detergents that are used and the high temperature of the waste water from dishwasher systems. This fat occurs in a similar kind of state as the fat in milk, which contains fat particles with a diameter of only 0.1 .mu.m to 10 .mu.m, which do not float to the top.
Furthermore, a conventional fat-separator has to be emptied and cleaned every two to four weeks, an intervention for which the operator of the installation is responsible. Fat-separators in butchers shops have to be cleaned at least once a week or, at the latest, when the fat storage container is full. As a general rule, fat-separators in industrial kitchens have to be emptied every two weeks. But the volume and quality of the waste water fluctuate even amongst industrial kitchens which prepare the same number of meals. Tests have shown that, because of differences in the types of foods and in the method of preparation, the fat content in the waste water from a hospital kitchen producing 1,000 meals per day is approx. 500 mg/l on average, for example, whilst the fat content in the waste water from an army kitchen is approx. 1,500 mg/l, i.e. three times more. The fat content per meal can range from 3 to 30 g. Depending on the type of kitchen, the fat-separators have to be drained more or less frequently. Regular draining of the fat-separator involves opening the latter and introducing a suction pipe leading from a waste disposal vehicle. The nauseous smell that occurs as the fat is sucked off causes a very unpleasant odour in the immediate vicinity of the installation. After the installation has been drained, it is cleaned with superheated steam. This essential maintenance work causes inconvenience as well as considerable recurrent costs. To reduce the volumes that have to be transported away, prior art fat-separating systems exist in which the separated fat is pressed into separate containers so that only the material actually separated off has to be transported away for disposal or recycling. Regular and expensive transport is still required, however, and this is an additional burden on the environment.